Co ty najlepszego robisz? => What do you do best?
This is the way Jeff Jarvis says it in this article:New rule: Cover what you do best. Link to the rest « BuzzMachine Quote about Jarvis from the comments: "Do what you do best and link to the rest." This is the famous February 2007 dictum of Google economy advocate Jeff Jarvis. Jarvis’s message is a plea for specialisation: stop trying to become the media of record, and instead concentrate on what you are good at.

How would you say "Co ty najlepszego robisz?" or "co tu robisz najlepszego" in English. I understand the general gist but am trying to figure out what the exact english equivalent would be.

thanks!

As Kajtek said it is more negative sense and you would rather say "Co ty tutaj najlepszego robisz?" it would literally mean "What the best are you doing here?", but it just means "What are you doing here?", but with the sense of feeling as you would say "What is it that you are doing here?", but like negative way as in "What the hell are you doing here?", like for example a child went into the kitchen and broken all the dishes and comes in the mother and says "Co ty tutaj najlepszego robisz?", sort of.